1. Field of the Invention
The present invention relates to aqueous polyurethane urea dispersions having integral functional groups and to coating compositions prepared therefrom, to a process for their preparation, and to their use in the preparation of coating compositions.
2. Description of Related Art
Coating compositions based on polyurethanes play a major role because of their excellent properties, such as, for example, high scratch resistance and low-temperature flexibility. Because of increasing ecological and other legal requirements, the solvent-free, aqueous polyurethanes are particularly important. Coatings based on polyurethane dispersions are used in various applications, such as, for example, the coating of textiles, the lacquering of plastics and motor vehicles or the coating of glass fibres.
Functionalised polymers for coatings generally provide the possibility of carrying out polymer-analogous reactions in a further process step in order to improve the properties of the coating. Attempts are frequently made to achieve a high molar mass, because a high molar mass generally has a positive effect on the final properties of the coating, such as, for example, solvent stability and hydrolytic stability.
U.S. Pat. No. 7,393,894 describes self-crosslinking polyurethane dispersions in which carbonyl-containing isocyanate-reactive compounds are used as structural components which, on drying, react with subsequently added crosslinkers such as, for example, dihydrazides and diamines. A disadvantage here is that a further component for crosslinking must be added in order to achieve the desired properties such as hydrolytic stability.
U.S. Pat. No. 6,462,127 describes fatty-acid-modified polyurethane dispersions which crosslink by the influence of oxygen (oxidative drying). A disadvantage of these systems is that crosslinking takes place comparatively slowly in a period of up to seven days.
U.S. Pat. No. 6,586,523 describes self-crosslinking polyurethane dispersions which consist of hydroxy-group-functional polyurethanes in which some of the isocyanate groups are blocked. A disadvantage of the polymers described therein is that the blocking agent is freed using elevated temperatures, which is undesirable from the point of view of work hygiene.